Certain products, such as insecticides and air sanitizers are commonly supplied in pressurized containers. The contents of the pressurized container are typically dispensed to the atmosphere by pressing down on a valve at the top of the container so that the contents of the container are emitted through a channel in the valve.
In some instances it is desirable that the contents of the container be automatically dispensed periodically. In other instances however, it is desirable to continuously expel the contents of the container at a slow rate over a long period of time. For example, the dispensing of a product for an extended period of time may negate the necessity of concentrated (i.e., puffs) of material resulting from the periodic dispensing of material. An additional advantage realized by a controlled continuous flow of the pressurized product is that the pressurized container may be left unattended for long periods of time while maintaining a continuous discharge of the product.
U.S. Pat. No. 6,540,155 to Yahav describes periodic dispensing of a spray and the amount of spray emitted at each period being controlled by setting the time in which the outlet is open, such as by operating the dispenser in response to a sensor which measures the level of material in the surroundings. The dispenser of Yahav is limited in that it requires a sensor to determine that the minimal level of material is not sufficient.
U.S. Pat. No. 3,756,472 to Vos, describes a micro-emitter for pressure packages comprising an apertured member disposed across the nozzle opening through which a fluid product in a pressurized container may be expelled. The apertured member serves to control the flow of the fluid and assist in droplet formation. However, Vos does not describe any preferred means of fabricating the micro-emitter and does not describe a micro-emitter that may be used replaceably with other types of spray dispensers.
Thus there remains a need for continued improvement of systems that allow for a slow release of a pressurized product in a cost effective manner, which can be provided, for example, in a continuous manner and without a power source (e.g. batteries).
The inventors of the present invention have determined that the use of micro-electromechanical (MEMS) fabrication techniques may be advantageously used to construct a microchip that allows for the continuous dispensing of material from a pressurized container, while overcoming many of the deficiencies of the prior art.
Micro-electromechanical systems (MEMS) is a process technology used to create tiny integrated devices or systems that combine mechanical and electrical components. MEMS are fabricated using integrated circuit (IC) batch fabrication techniques and can range in size from a few micrometers to a few millimeters. MEMS takes advantage of silicon's mechanical properties, or its electrical and mechanical properties, and MEMS components are generally fabricated by sophisticated manipulations of silicon (and other substrates) using micromachining processes.
MEMS, with its batch fabrication techniques, enables components and devices to be manufactured with increased performance and reliability, and provide the advantages of reduced physical size, volume, weight, and cost. To date, MEMS have found commercial success in applications such as automotive airbag sensors, medical pressure sensors, inkjet print heads, and overhead projection displays and are being developed for use as bioMEMS, in optical communications (MOEMS) and as radio frequency (RF) MEMS.
MEMS fabrication uses high volume IC-style batch processing that involves the addition or subtraction of two-dimensional layers on a substrate based on photolithography and chemical etching. As a result, the 3D aspect of MEMS devices is due to patterning and interaction of the 2D layers. Additional layers can be added using a variety of thin film and bonding techniques as well as by etching through sacrificial “spacer layers.”
Photolithography is a photographic technique that is used to transfer copies of a master pattern, typically a circuit layout in IC applications, onto the surface of a substrate of some material. The substrate is covered with a thin film of some material, usually silicon dioxide, in the case of silicon wafers, on which a pattern of holes will be formed. A thin layer of an organic polymer, which is sensitive to ultraviolet radiation, is then deposited on the oxide layer; this is called a photoresist. A photomask, consisting of a transparent glass plated with an opaque pattern, is then placed in contact with the photoresist coated surface. The wafer is exposed to the ultraviolet radiation, transferring the pattern on the mask to the photoresist which is then developed in a way similar to the process used for developing photographic films. The radiation causes a chemical reaction in the exposed areas of the photoresist, of which there are two types—positive and negative. Positive photoresist is strengthened by UV radiation while negative photoresists are weakened. On developing, the rinsing solution removes either the exposed areas or the unexposed areas of photoresist, leaving a pattern of bare and photoresist-coated oxides on the wafer surface. The resulting photoresist pattern is either the positive or negative image of the original pattern of the photomask.
A chemical (i.e., hydrochloric acid) is used to attack and remove the uncovered oxide from the exposed areas of the photoresist. The remaining photoresist is subsequently removed with a chemical that attacks the photoresist but not the oxide layer on the silicon (i.e., hot sulfuric acid), leaving a pattern of oxide on the silicon surface. The final oxide pattern is either a positive or negative copy of the photomask pattern and serves as a mask in subsequent processing steps. The oxide then serves as a subsequent mask for either further additional chemical etching, creating deeper 3D pits or new layers on which to build further layers, resulting in an overall 3D structure or device.
The most common substrate material for micromachining is silicon for a variety of reasons, including: 1) silicon is abundant, inexpensive, and can be processed to a high degree of purity; 2) silicon can be easily deposited in thin films; and 3) silicon microelectronics circuits are batch fabricated (a silicon wafer contains hundreds of identical chips, not just one).
Although silicon is most commonly used, other substrate materials, including crystalline semiconductors such as germanium and gallium arsenide, and non-semiconductor substrate materials such as metals, glass, quartz, crystalline insulators, ceramics, and polymers, have also been suggested for use in MEMS fabrication.
In order to form more complex and larger MEMS structures, micromachined silicon wafers can be bonded to other materials in a process known as fusion bonding, which is a technique that enables virtually seamless integration of multiple layers and relies on the creation of atomic bonds between each layer. In the case of glass to wafer bonding, a direct bond is created by heat and pressure.
MEMS has many applications in microfluidics with many of the key building blocks such as flow channels, pumps, and valves being amenable to being fabricated using micromachining techniques. The inventors of the present invention have determined that MEMS fabrication techniques may be used to produce microchips that are usable to provide the slow release of contents from an aerosol container in a cost-effective and predictable manner. To that end, the inventors of the instant invention have used MEMS fabrication techniques to develop a microchip that is usable with a dispensing means to control the flow of fluid from a pressurized container of the fluid.